Semiconductor light emitting element

ABSTRACT

Is provided a resonant cavity type light emitting diode having excellent humidity durability and a light output unsaturated even several 10 mA., which is suitable for mass production. The semiconductor light emitting element has a resonator formed by one set of multi-layer reflecting films disposed at a constant distance on a GaAs substrate inclined at an angle of not less than 2 degrees in the direction [011] or [0-1-1] from the plane (100) and a light emitting layer disposed at a loop position of a standing wave in the resonator, wherein a multi-layer reflecting film disposed on the GaAs substrate side is composed of plural layers of Al x Ga 1-x As (0≦x≦1) and a multi-layer reflecting film disposed on the opposite side of the GaAs substrate is composed of plural layers of Al y Ga z In 1-y-z P (0≦y≦1, 0≦z≦1), thereby achieving an improved humidity durability and an increased reflection factor by increasing the number of the reflection layers.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor light emitting elementand, more specifically, to a resonant cavity type light emitting diodethat possesses an excellent humidity durability and has light outputunsaturated even at an injection current of not more than several 10 mA.

In recent years, semiconductor light emitting elements have widely usedfor optical communications and information semiconductor light emittingelement information display panels. In this connection, concentrateddevelopment efforts have been placed on creating semiconductor lightemitting elements having high efficiency of light emission andhigh-speed response in particular for optical communication.Conventional surface-emitting type light emitting diodes haveinsufficient response characteristics that are limited (LED) to 100Mbps-200 Mbps. Accordingly, there have been developed new semiconductorlight emitting elements so called resonant cavity type light emittingdiodes (LED). The resonant cavity type LED is a semiconductor lightemitting element which controls spontaneous light-emission by setting alight emitting layer at a loop (anti-node) of standing wave produced ina resonator composed of two mirrors, thus achieving high speed responseand high efficiency of light emission. Prior arts are described inJapanese Patent Publication No. 2744503 and U.S. Pat. No. 5,226,053.With advanced application of optical fibers made of plastic materials(POF) such as PMMA for relatively short distance communications, therehas been developed a new resonant cavity type LED that has alight-emission layer made of a AlGaInP semiconductor capable ofeffectively emitting light with wavelengths of 650 nm, which correspondsto a low-loss frequency range of the POF. This type LED is disclosed inIEEE Photonics Technology Letters, Vol. 10, No. 12, December 1998 (HighBrightness Visible Resonant Cavity Light Emitting Diode).

The conventional resonant cavity type LED uses multi-layer reflectingfilm of AlGaAs material as a mirror composing a resonator, so it has alayer of AlGaAs having a mixed AlAs or Al crystal ratio of about 1 inthe neighborhood of its surface electrode, which may decrease itshumidity durability. Since current injected from the surface isinsufficiently diffused only by a distributed Bragg reflector (DBR)having thickness of about 1 μm, the light output of the LED is saturatedeven with injected current of several 10 mA. To compensate the aboveinsufficiency, the surface electrode is made in the form of a honeycombor meshed electrode of several micro-millimeters (μm) in width. However,this solution arose a new problem with breaking electrodes in theproduction process. The proposed element was not suited formass-production.

SUMMARY OF INVENTION

An object of the present invention is to provide a resonant cavity typelight emitting diode that has excellent humidity durability and a lightoutput unsaturated even with several 10 mA and is suitable for massproduction.

Another object of the present invention is to provide a semiconductorlight emitting element having a resonator composed of paired multi-layerreflecting films disposed at a constant distance on a GaAs substrate andhaving a light emitting layer disposed at the loop position of astanding wave in the resonator, wherein relative to the light emittinglayer, a multi-layer reflecting film disposed on the GaAs substrate sideis composed of plural layers of Al_(x)Ga_(1-x)As (0≦x≦1) and amulti-layer reflecting film opposite to the GaAs substrate side iscomposed of plural layers of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).

In the above semiconductor light emitting element, relative to the lightemitting layer, a multi-layer reflecting film of Al_(x)Ga_(1-x)As(0≦x≦1), disposed on the GaAs substrate side, has a very smalldifferential thermal expansion coefficient relative to the GaAssubstrate. Consequently, the transition due to a difference oftemperatures before and after crystal growth may not occur. This makesit possible for the element to easily obtain a high reflection factor byincreasing the number of reflecting films.

Relative to the light emitting layer, the multi-layer reflecting filmopposite to the GaAs substrate side reflecting film is formed ofAl_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1). This film has a maximum contentof Al when matching the lattice of the GaAs substrate, which value is25%, i.e., merely a half of 50% for Al_(x)Ga_(1-x)As (0≦x≦1). This canconsiderably improve the humidity durability of the element. Formulti-layer reflecting film of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1),the transition is apt to occur due to a difference of thermal expansioncoefficients between the film and the GaAs substrate when the number oflayers exceeds 20-30 pairs. For the resonant cavity type light emittingdiode, the multi-layer reflecting film opposite to the GaAs substrateside need not have a high reflection factor in comparison with themulti-layer reflecting film on the GaAs substrate side, so usually itneed not have layers exceeding 20 pairs and may therefore be free fromthe occurrence of the transition.

Another object of the present invention is to provide a semiconductorlight emitting element whose light emitting layer is composed of asingle- or multi-layer film of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).

The above semiconductor element can emit light with wavelengths of about550 nm-680 nm from its light emitting layer of Al_(y)Ga_(z)In_(1-y-z)P(0≦y≦1,0≦z≦1).

Another object of the present invention is to provide a semiconductorlight emitting element in which a current constricting structure of aninsulation layer or the same-conductive type layer as the GaAs substrateis disposed above the light emitting layer.

Owing to the current constricting structure formed by an insulationlayer or the same-conduction type layer as the GaAs substrate above thelight emitting layer, the semiconductor light emitting element canincrease a current density, achieving high internal quantum efficiency.The absence of an electrode for a bonding pad on the light emittingportion improves the light emitting efficiency of the element.Furthermore, the use of the semiconductor light emitting element foroptical communications realizes higher efficiency of coupling withoptical fibers owing to a reduced size of its light emitting portion.

Another object of the present invention is to provide a semiconductorlight emitting element having the current constricting structure formedby a layer of Al_(x)Ga_(1-x)As (0≦x≦1).

In the semiconductor light emitting element, the current constrictinglayer matching the lattice of the GaAs substrate can be formed through acrystal growth process.

Another object of the present invention is to provide a semiconductorlight emitting element that has the current constricting structureformed by a layer of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).

In this semiconductor light emitting element, the current constrictinglayer can be formed through the growth of crystals. The layer ofAl_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1) can become transparent(light-transmittable) to permit the passage of light with wavelengths ofmore than 550 nm, thus assuring effective emission of the light.

Another object of the present invention is to provide a semiconductorlight emitting element that has a current diffusion layer formed abovethe layer forming the current constricting structure.

Owing to the presence of the current diffusion layer formed above thecurrent constricting layer, the semiconductor light emitting element canuniformly emit light at a reduced operating voltage.

A further object of the present invention is to provide a semiconductorlight emitting element that has the current diffusion layer formed by alayer of Al_(x)Ga_(1-x)As (0≦x≦1).

The semiconductor light emitting element can become transparent (lighttransmittable) to permit the passage of light emitted with wavelengthsof more than 590 nm with due consideration of humidity durability. Theelement can thus emit the light at an increased efficiency.

A still further object of the present invention is to provide asemiconductor light emitting element that has the current diffusionlayer formed by a layer of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).

The semiconductor light emitting element becomes transparent (lighttransmittable) to permit the passage of light with wavelengths of morethan 550 nm. Therefore, the element can effectively emit the light at anincreased efficiency.

Another object of the present invention is to provide a semiconductorlight emitting element that has the current diffusion layer formed by atransparent electrode having the transmittance of the emitted light,which transmittance is not less than 50%.

The semiconductor light emitting element containing the currentdiffusion layer formed by a light-transmitting electrode oftransmittance of 50% or more can be operated at an operating voltagebeing lower than that of the semiconductor light emitting element havinga current diffusion layer formed by semiconductor material.

Another object of the present invention is to provide a semiconductorlight emitting element whose GaAs substrate has a surface inclined at anangle of not less than 2 degrees in the direction [011] or [0-1-1] fromthe plane (100).

The semiconductor light emitting element having the GaAs substrateinclined at an angle of not less than 2 degrees in the direction [011]or [0-1-1] from the plane (100) can achieve a high reflection efficiencyof the multi-layer reflecting film that has the reduced number of layerssince the reflecting film of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1) canbe easily formed with a mirror surface disposed opposite to the GaAssubstrate side reflecting film with the light emitting layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a plan view and a sectional view taken on line X-Yof FIG. 1A, respectively, of a semiconductor light emitting elementaccording to a first embodiment of the present invention.

FIG. 2 is a sectional view of the semiconductor light emitting elementshown in FIGS. 1A and 1B, which is midway through its manufacturingprocess.

FIGS. 3A and 3B are a plan view and a sectional view taken on line X-Yof FIG. 3A, respectively, of the semiconductor light emitting element ofFIGS. 1A and 1B, which is midway through its manufacturing process.

FIGS. 4A and 4B are a plan view and a sectional view taken on line X-Yof FIG. 4A, respectively, of a semiconductor light emitting elementaccording to a second embodiment of the present invention.

FIG. 5 is a sectional view of the semiconductor light emitting elementshown in FIGS. 4A and 4B, which is midway through its manufacturingprocess.

FIGS. 6A and 6B are a plan view and a sectional view taken online X-Y ofFIG. 6A, respectively, of the semiconductor light emitting element ofFIGS. 4A and 4B, which is midway through its manufacturing process.

FIGS. 7A and 7B are a plan view and a sectional view taken on line X-Yof FIG. 7A, respectively, of a semiconductor light emitting elementaccording to a third embodiment of the present invention.

FIG. 8 is a sectional view of the semiconductor light emitting elementshown in FIGS. 7A and 7B, which is midway through its manufacturingprocess.

FIGS. 9A and 9B are a plan view and a sectional view taken on line X-Yof FIG. 9A, respectively, of the semiconductor light emitting element ofFIGS. 7A and 7B, which is midway through its manufacturing process.

FIGS. 10A and 10B are a plan view and a sectional view taken on line X-Yof FIG. 10A, respectively, of a semiconductor light emitting elementaccording to a fourth embodiment of the present invention.

FIG. 11 is a sectional view of the semiconductor light emitting elementshown in FIGS. 10A and 10B, which is midway through its manufacturingprocess.

FIGS. 12A and 12B are a plan view and a sectional view taken on line X-Yof FIG. 12A, respectively, of the semiconductor light emitting elementof FIGS. 10A and 10B, which is midway through its manufacturing process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will be described belowwith reference to FIGS. 1 to 12.

(Embodiment 1)

FIG. 1A shows in plan a semiconductor light emitting element that is afirst embodiment of the present invention and FIG. 1B is a sectionalview taken on line X-Y of FIG. 1A.

FIG. 2 is a sectional view of the semiconductor light emitting elementaccording to the first embodiment, which is midway through itsmanufacturing process.

FIG. 3A is a plan view of a semiconductor light emitting elementaccording to the first embodiment, which is midway through itsmanufacturing process. FIG. 3B is a sectional view taken on line X-Y ofFIG. 3A.

The semiconductor light emitting element is of the AlGaInP group andhas, as shown in FIG. 2, a n-type GaAs substrate 1 inclined at an angleof 2 degrees in the direction [011] or [0-1-1] from its plane (100) andhas a series of layers deposited on the substrate 1 by an MOCVD (MetalOrganic Chemical Vapor Deposition) method. Namely, an n-type GaAs bufferlayer 2 (1 μm thick layer), a DBR (distributed bragg reflector) 3consisting of 30 paired layers of n-type AlAs and n-typeAl_(0.5)Ga_(0.5)As, a first clad layer 4 of n-type(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a quantum well active layer 5consisting of a well layer of GaInP and a barrier layer of(Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a second clad layer 6 of p-type(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a DBR 7 consisting of 12 pairs of ap-type (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P layer and a p-typeAl_(0.5)In_(0.5)P layer, an intermediate layer 8 of p-type(Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P (0.1 μm thick layer) and a contactlayer 9 of p-type GaAs (1 μm thick layer) are deposited in subsequentlayers in the described order on the GaAs substrate 1 by the MOCVDmethod.

The DBR 3 consisting of 30 pairs of an n-type AlAs and an n-typeAl_(0.5)Ga_(0.5)As layer and the DBR 7 consisting of 12 pairs of ap-type (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P layer andap-typeAl_(0.5)In_(0.5)P layer are formed each to have a center reflectionspectrum of 650 nm. A resonator formed by these DBR 3 and DBR 7 isadjusted in its length to have a resonant wavelength of 650 nm. In theembodiment 1, the length of the resonator is adjusted to 1.5 times thewavelength. Furthermore, the quantum well active layer 5 composing alight emitting layer is positioned at a loop position of a standing waveproduced in the resonator and adjusted to obtain a peak wavelength 650nm of light to be emitted from there.

Then, as shown in FIGS. 3A and 3B, a SiO₂-film 10 is deposited on awafer surface by the CVD method and a 70-μm diameter circular currentchannel is formed therein by photolithography and dilution HF etching.

Returning to FIGS. 1A and 1B, AnZu/Mo/Au is sputtered onto the p-typeGaAs contact layer 9 and the SiO₂ film 10 layer and a surface electrodeis formed thereon by photolithographic patterning. Conventionally, thereis a 1-3-μm thick layer between the surface electrode 11 and the lightemitting layer, wherein current is diffused insufficiently. Accordingly,the shown embodiment has an electrode formed in the form of a ringhaving the width of several micro-millimeters (μm) as shown in FIG. 1A,through which current can be uniformly injected into the light emittinglayer. Therefore, the occurrence of light that cannot be output by thepresence of the electrode can be suppressed. A p-type electrode 11 isthen formed by thermal treating. The GaAs substrate is ground at itsopen surface to its thickness of 280 μm, whereon AuGe/Au is depositedand thermally treated to form an n-type electrode 12 thereon.

The thus obtained semiconductor light emitting has a multi-layerreflecting film (DBR3) with a total film thickness of 3 μm on the sidenear to the GaAs substrate 1 but may be free from the occurrence of acamber or a dark line of the film owing to a small difference in thermalexpansion coefficients of the film and the substrate 1. The film of 30paired layers achieves an increased light reflection coefficient of 99%.Relative to the emitting layer consisting of the quantum well activelayer 5, the multi-layer reflecting film (DBR7) disposed on the sideopposite to the GaAs substrate 1 is formed of material AIGaInP and hassurface layers of Al_(0.5)In_(0.5)P with a maximal content of Al, whichhas a sufficient humidity durability. The multi-layer reflecting filmshows a peak reflection factor of about 70%, which value is sufficientfor the resonant cavity structure of the element. The semiconductorlight emitting element was tested for operation with current 50 mA at anambient temperature of 80° C. and relative humidity of 85%. The lightoutput of the element was measured after 1000 hours of test duration andit achieved 90% of its initial output. The element has a currentconstricting structure formed by the SiO₂ film 10 and can thereforeobtain a high internal quantization efficiency and a high externalradiation efficiency. Namely, the useful initial light produced from theelement achieved 1.6 mW at 20 mA, which is sufficient for use in theoptical communications over plastic optical fiber (POF) networks.

(Embodiment 2)

FIG. 4A is a plan view of a semiconductor light emitting elementaccording to a second embodiment of the present invention and FIG. 4B isa sectional view taken on line X-Y of FIG. 4A.

FIG. 5 is a sectional view of the semiconductor light emitting element(embodiment 2) being midway through its manufacturing process.

FIG. 6A is a plan view of the semiconductor light emitting element(embodiment 2) being midway through its manufacturing process, and FIG.6B is a sectional view taken on line X-Y of FIG. 6A.

The shown semiconductor light emitting element is of the AlGaInP groupand has, as shown in FIG. 5, a n-type GaAs substrate 21 inclined at anangle of 15 degrees in the direction [011] or [0-1-1] from the plane(100) and has layers subsequently deposited thereon by the MOCVD method.Namely, an n-type GaAs buffer layer 22 (1 μm thick layer), a DBR(distributed bragg reflector) 23 consisting of 30 paired layers ofn-type AlAs and n-type Al_(0.5)Ga_(0.5)As, a first clad layer 24 ofn-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a quantum well active layer 25consisting of a well layer of GaInP and a barrier layer of(Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a second clad layer 26 of p-type(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a DBR 27 consisting of 12 pairs of ap-type (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P layer and a p-typeAl_(0.5)In_(0.5)P layer, an etching stop layer 28 of p-type(Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P (0.5 μm thick layer), a currentconstricting layer 29 of n-type GaAs (0.3 μm thick layer), a protectivelayer 30 of n-type (Al_(0.3)Ga_(0.7))_(0.5)In_(0.5)P (0.1 μm thicklayer) and a cap layer 31 of n-type GaAs (0.01 μm thick layer) aredeposited in subsequent layers in the described order on the substrate21 by the MOCVD method.

The DBR 23 consisting of 30 pairs of an n-type AlAs layer and an n-typeAl_(0.5)Ga_(0.5)As layer and the DBR 27 consisting of 12 pairs of ap-type (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P layer and a p-typeAl_(0.5)In_(0.5)P layer are formed each to have a center reflectionspectrum of 650 nm. A resonator formed by these two DBRs 23 and 27 isadjusted in its length to have a resonant wavelength of 650 nm. In theembodiment 2, the length of the resonator is adjusted to 1.5 times thewavelength. Furthermore, the quantum well active layer 25 composing alight emitting layer is disposed at a loop position of a standing waveproduced in the resonator and adjusted to obtain a peak wavelength 650nm of light to be emitted from there.

Then, as shown in FIGS. 6A and 6B, the cap layer 31 is removed with asulfuric acid/hydrogen peroxide etchant and the n-type(Al_(0.3)Ga_(0.7))_(0.5)In_(0.5)P protective layer 30 and the n-typeGaAs current constricting layer 29 are etched by photo-lithographicallyetching and by phosphoric acid and sulfuric acid/hydrogen peroxideetchant until it reaches the etching stop layer 28. A circular currentpassage having a diameter of 70 μm is thus formed.

Returning to FIGS. 4A and 4B, the p-type Al_(0.5)Ga_(0.5)As currentdiffusion layer 32 (7 μm thick) is grown again on the n-type(Al_(0.3)Ga_(0.7))_(0.5)In_(0.5)P protective layer 30 and the p-type(Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P etching stop layer 28, then AnZu/Mo/Auis sputtered onto the p-type Al_(0.5)Ga_(0.5)As current diffusion layer32 and a surface electrode is formed by photo-lithographically etchingand etching with an Au-etchant and an ammonia/hydrogen peroxide etchant.A p-type electrode 33 is obtained by thermal treatment. The GaAssubstrate is ground at its surface to the thickness of about 280 μm,then metal AuGe/Au is deposited to the ground surface of the substrateand thermally treated to form thereon an n-type electrode 34.

The semiconductor light emitting element thus produced has themulti-layer reflecting film similar in structure to that of theembodiment 1 but uses the GaAs substrate inclined at an angle of 15degrees in the direction [011] from the plane (100) while the GaAssubstrate of the embodiment 1 is inclined at an angle of 2 degrees inthe same direction. Namely, the embodiment 2 can obtain higher surfacequality of the substrate. Consequently, the reflection factor of themulti-layer reflecting film (DBR27) made of AlGaInP group material,which is opposite to the GaAs substrate side reflecting film (DBR 21)with the light emitting layer between them, achieves an improvedreflection factor of 75% as compared with the reflection factor (70%) ofthe equivalent film of embodiment 1. The element of the embodiment 2 hassufficient humidity durability. The semiconductor light emitting elementaccording to the embodiment 2 was tested for operation with current of50 mA at an ambient temperature of 80° C. and humidity of 85% and itslight output after 1000 hours of the test duration was measured. Themeasured light output corresponds to 90% of its initial light output.The element also achieved a sufficient initial light output of 2.2 mW at20 mA. Owing to the current diffusion surface layer 32 ofAl_(0.5)Ga_(0.5)As, the semiconductor light emitting element of theembodiment 2 can increase its light output to 4.2 mW in proportion toits operating current increasing to 40 mA while the semiconductor lightemitting element of the embodiment 1 shows a somewhat saturated outputof 2 mW with the operating current increasing to 40 mA. The embodiment 2also achieved a reduced operating voltage of 2.1 V with a current of 20mA as compared with the operating voltage of 2.2 V of the embodiment 1with the same current. All the above-described improvements have beenobtained by the effect of the Al_(0.5)Ga_(0.5)As current diffusion layer32 allowing the current to uniformly be injected into the light emittinglayer.

(Embodiment 3)

FIG. 7A is a plan view, respectively, of a semiconductor light emittingelement according to a third embodiment of the present invention, andFIG. 7B is a sectional view taken on line X-Y of FIG. 7A.

FIG. 8 is a sectional view of the semiconductor light emitting element(embodiment 3) being midway through its manufacturing process.

FIG. 9A is a plan view of the semiconductor light emitting element(embodiment 3) being midway through its manufacturing process, and FIG.9A is a sectional view taken on line X-Y of FIG. 9A.

The shown semiconductor light emitting element is of the AlGaInP groupand has, as shown in FIG. 8, a n-type GaAs substrate 41 inclined at anangle of 15 degrees in the direction [011] or [0-1-1] from the plane(100) and has a series of layers deposited thereon by the MOCVD method.Namely, an n-type GaAs buffer layer 42 (1 μm thick layer), a DBR(distributed bragg reflector) 43 consisting of 70 paired layers ofn-type AlAs and n-type Al_(0.7)Ga_(0.3)As, a first clad layer 44 ofn-type (Al_(0.7)Ga_(0.3))_(0.3)In_(0.5)P, a quantum well active layer 45consisting of a well layer of (Al_(0.3)Ga_(0.7))_(0.5)In_(0.5)P and abarrier layer of (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a second clad layer46 of p-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a DBR 47 consisting of18 pairs of a p-type (Al_(0.4)Ga_(0.6))_(0.5)In_(0.5)P layer and ap-type Al_(0.5)In_(0.5)P layer, an intermediate layer 48 of p-typeAlGaInP (0.15 μm thick layer), a first current diffusion layer 49 ofp-type AlGaInP (1 μm thick layer), a current constricting layer 50 ofn-type AlGaInP (0.3 μm thick layer) and a cap layer 51 of n-type GaAs(0.01 μm thick layer) are deposited in subsequent layers in thedescribed order on the substrate 41 by the MOCVD method.

The DBR 43 consisting of 70 pairs of an n-type AlAs layer and an n-typeAl_(0.7)Ga_(0.3)As layer and the DBR 47 consisting of 18 pairs of ap-type (Al_(0.4)Ga_(0.6))_(0.5)In_(0.5)P layer and a p-typeAl_(0.5)In_(0.5)P layer are formed each to have a center reflectionspectrum of 570 nm. A resonator formed by these two DBRs 43 and 47 isadjusted in its length to have a resonant wavelength of 570 nm. In theembodiment 3, the length of the resonator is adjusted to 1.5 times thewavelength. Furthermore, the quantum well active layer 45 is disposed ata loop position of a standing wave produced in the resonator andadjusted to obtain a peak wavelength 570 nm of light to be emitted fromthere.

Then, as shown in FIGS. 9A and 9B, the n-type GaAs cap layer 51 isremoved with a sulfuric acid/hydrogen peroxide etchant and the n-typeAlGaInP current constricting layer 50 is etched byphoto-lithographically etching and by a sulfuric acid/hydrogen peroxideetchant until it reaches the p-type AlGaInP first current diffusionlayer 49. A circular current passage having a diameter of 70 μm is thusformed.

Returning to FIGS. 7A and 7B, the second p-type AlGaInP currentdiffusion layer 52 (7 μm thick) is grown again on the p-type AlGaInPcurrent constricting layer 50 and the first p-type AlGaInP currentdiffusion layer 49.

A metal coat of AuBe/Au is deposited onto the second p-type AlGaInPcurrent diffusion layer and a surface electrode isphoto-lithographically patterned thereon and etched with an Au-etchant.A p-type electrode 53 is obtained by further thermal treatment. The GaAssubstrate is ground at its surface to the thickness of about 280 μm,then AuGe/Au is deposited onto the ground surface of the substrate andthermally treated to form thereon an n-type electrode 54.

The semiconductor light emitting element thus produced has the AlGaAsmulti-layer reflecting film (DBR43) (on the GaAs substrate side), whichtotal thickness is about 71 μm and greater than those of the embodiments1 and 2. However, the layer has a very small difference in thermalexpansion from the substrate and therefore does not cause a camber ofthe substrate and a dark line thereon. The film composed of 70 pairs oflayers realizes an improved reflection factor of 99% or more. Themulti-layer reflecting film (DBR 47), which is disposed opposite to GaAssubstrate side 41, is made of AlGaInP-material possessing sufficienthumidity durability like the embodiments 1 and 2.

The semiconductor light emitting element according to the embodiment 3was tested for operation with current of 50 mA at an ambient temperatureof 80° C. and humidity of 85% and its light output after 1000 hours ofthe test duration was measured. The measured light output corresponds to105% of its initial light output (0.4 mW).

(Embodiment 4)

FIG. 10A is a plan view of a semiconductor light emitting elementaccording to a fourth embodiment of the present invention and FIG. 10Bis a sectional view taken on line X-Y of FIG. 10A.

FIG. 11 is a sectional view of the semiconductor light emitting element(embodiment 4) being midway through its manufacturing process.

FIG. 12A is a plan view of the semiconductor light emitting element(embodiment 4) being midway through its manufacturing process, and FIG.12B is a sectional view taken on line X-Y of FIG. 12A.

The shown semiconductor light emitting element is of the AlGaInP groupand has, as shown in FIG. 11, a n-type GaAs substrate 61 inclined at anangle of 15 degrees in the direction [011] or [0-1-1] from the plane(100) has a series of layers deposited thereon by the MOCVD method. Thatis, an n-type GaAs buffer layer 62 (1 μm thick layer), a DBR(distributed bragg reflector) 63 consisting of 30 paired layers ofn-type AlAs and n-type Al_(0.5)Ga_(0.5)As, a first clad layer 64 ofn-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a quantum well active layer 65consisting of a well layer of GaInP and a barrier layer of(Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a second clad layer 66 of p-type(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a DBR 67 consisting of 12 pairs of ap-type (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P layer and a p-typeAl_(0.5)In_(0.5)P layer, an intermediate layer 68 of p-type(Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P (0.1 μm thick layer) and a contactlayer 69 of p-type GaAs (0.005 μm thick layer) are subsequentlydeposited in layers in the described order on the substrate 61 by theMOCVD method.

The DBR 63 consisting of 30 pairs of an n-type AlAs layer and an n-typeAl_(0.5)Ga_(0.5)As layer and the DBR 67 consisting of 12 pairs of ap-type (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P layer and a p-typeAl_(0.5)In_(0.5)P layer are formed each to have a center reflectionspectrum of 650 nm. A resonator formed by these two DBRs 63 and 67 isadjusted in its length to have a resonant wavelength of 650 nm.Furthermore, the quantum well active layer 65 is disposed at a loopposition of a standing wave produced in the resonator and adjusted toobtain a peak wavelength 650 nm of light to be emitted from there.

Then, as shown in FIGS. 12A and 12B, a SiO₂-film 70 is formed on a wafersurface by the CVD method and a circular current channel of 70 μm indiameter is formed therein by photolithography and etching with dilutedHF. Namely, the SiO₂-film 70 forms a current constricting structure.

Returning to FIGS. 10A and 10B, the GaAs substrate 61 is ground at itssurface to the thickness of about 280 μm, then metal AuGe/Au isdeposited onto the ground surface of the substrate to form thereon ann-type electrode 71. A surface electrode is formed by an ITO film 72 onthe P-type GaAs contact layer 69 and the Si0 ₂ film 70. Namely, the ITOfilm 72 serves as a current diffusion layer. A bonding pad 73 of Ti/Auis then formed thereon.

The semiconductor light emitting element thus produced has the samestructure of the multi-layer reflecting films as those of the embodiment2 but achieved a decreased operating voltage of 1.9V at 20 mA, which islower than by 0.2V the operating voltage 2.1V of the embodiment 2. Thep-type GaAs contact layer 69 and the ITO film 72 have a 70%-transmissioncoefficient of light with wavelengths of 650 nm. The measured lightoutput of the semiconductor light emitting element according to theembodiment 4 is 1.5 mW at 20 mA. The light output of the element testedfor operation at 50 mA for 1000 hours at an ambient temperature of 80°C. and humidity of 85% is 90% of the initial output. The test resultshows the element possesses the sufficient humidity durability.

As is apparent from the foregoing, the semiconductor light emittingelement according to the present invention has a resonator composed ofone set of multi-layer reflecting films disposed at a constant distanceon a GaAs substrate and has a light emitting layer disposed at aposition of a standing-wave loop in the resonator for emitting light inthe direction perpendicular to the substrate, wherein a multi-layerreflecting film disposed on the one side of the light emitting layerfrom the GaAs substrate side is composed of plural layers ofAl_(x)Ga_(1-x)As (0≦x≦1) and a multi-layer reflecting film on theopposite side of the light emitting layer is composed of plural layersof Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).

In the above semiconductor light emitting element, relative to the lightemitting layer, a multi-layer reflecting film of Al_(x)Ga_(1-x)As(0≦x≦1), disposed on the GaAs substrate side, has a very smalldifferential thermal expansion coefficient relative to the GaAssubstrate. Consequently, the transition due to a difference oftemperatures before and after crystal growth may not occur. This makesit possible for the element to easily obtain a high reflection factor byincreasing the number of reflecting films.

Since the multi-layer reflecting film disposed opposite to the GaAssubstrate side multi-layer reflecting film with the light emitting layerbetween them is formed of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1), it mayhave a maximum content of Al when matching the lattice with the GaAssubstrate, which value is 25%, i.e., merely a half of 50% forAl_(x)Ga_(1-x)As (0≦x≦1). This can considerably improve the humiditydurability of the element. For the multi-layer reflecting film ofAl_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1), the transition is apt to occurdue to a difference of thermal expansion coefficients between the filmand the GaAs substrate when the number of layers exceeds 20-30 pairs.For the resonant cavity type light emitting diode (LED), the multi-layerreflecting film on the opposite side need not have a high reflectionfactor in comparison with the multi-layer reflecting film on the GaAssubstrate side, so usually it need not have layers exceeding 20 pairsand may therefore be free from the occurrence of the transition.

A semiconductor light emitting element according to an aspect of thepresent invention has a light emitting layer formed at the loop positionof the standing-wave in the resonant cavity formed by a pair ofmulti-layer reflecting films disposed at a constant distance on the GaAssubstrate, which light emitting layer is composed of a single- ormulti-layer film of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1) and can emitlight with wavelengths of 550 nm-680 nm.

A semiconductor light emitting element according to another aspect ofthe present invention has an insulation layer or a current constrictingstructure formed by a layer having the same conduction as the GaAssubstrate, which layer is disposed above the light emitting layer. Owingto the above current constricting structure above the light emittinglayer, the semiconductor light emitting element can increase a currentdensity, achieving high internal quantum efficiency. The absence of anelectrode for a bonding pad above the light emitting portion improvesthe light emitting efficiency of the semiconductor light emittingelement. Furthermore, the use of the semiconductor light emittingelement for optical communications realizes a high efficiency ofcoupling with optical fibers owing to a reduced size of its lightemitting portion.

A semiconductor light emitting element according to another aspect ofthe present invention has a current constricting structure formed by alayer of Al_(x)Ga_(1-x)As (0≦x≦1) above the light emitting layer. Thiscurrent constricting layer is of the same conduction type as the GaAssubstrate and can therefore be formed matching the lattice with that ofthe GaAs substrate through the crystal growing process.

A semiconductor light emitting element according to another aspect ofthe present invention has the current constricting structure formed by alayer of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1). This currentconstricting layer is of the same conduction type as the GaAs substrate.This semiconductor light emitting element can form a currentconstricting layer matching the lattice of the GaAs substrate throughthe growth of crystals. The layer of Al_(y)Ga_(z)In_(1-y-z)P(0≦y≦1,0≦z≦1) can become transparent to permit the passage of light withwavelengths of not more than 550 nm, assuring effective emission of thelight.

A semiconductor light emitting element according to another aspect ofthe present invention has a current diffusion layer formed above thelayer forming the current constricting structure formed by an insulationlayer or the same-conductive type layer as the GaAs substrate above thelight emitting layer. Owing to the presence of the current diffusionlayer formed above the current constricting structure, the semiconductorlight emitting element can uniformly emit light at a reduced operatingvoltage.

A semiconductor light emitting element according to another aspect ofthe present invention has the current diffusion layer formed by a layerof Al_(x)Ga_(1-x)As (0≦x≦1) above the layer forming the currentconstricting structure formed by an insulation layer or thesame-conductive type layer as the GaAs substrate above the lightemitting layer. The current diffusion layer of Al_(x)Ga_(1-x)As (0≦x≦1)can become transparent (light-transmittable) to permit the passage oflight emitted with wavelength of more than 590 nm with due considerationof humidity durability. The element can thus emit the light at anincreased efficiency.

A semiconductor light emitting element according to another aspect ofthe present invention has the current diffusion layer formed by a layerof Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1). This current diffusion layeris above the layer forming the current constricting structure formed byan insulation layer or the same-conductive type layer as the GaAssubstrate above the light emitting layer. The semiconductor lightemitting element becomes transparent to permit the passage of light withwavelengths of more than 550 nm. Therefore, the element can effectivelyoutput the light produced with the wavelength of 550 nm.

A semiconductor light emitting element according to another aspect ofthe present invention has the current diffusion layer formed by atransparent (light-transmittable) electrode having the transmittance ofnot less than 50% of the emitted light. This current diffusion layer isabove the layer forming the current constricting structure formed by aninsulation layer or the same-conductive type layer as the GaAs substrateabove the light emitting layer. The semiconductor light emitting elementcontaining the current diffusion layer formed by a light-transmittingelectrode of transmittance of 50% or more can be operated at a reducedoperating voltage lower than that of the semiconductor light emittingelement having a current diffusion layer formed by semiconductormaterial. A semiconductor light emitting element according to anotheraspect of the present invention has the GaAs substrate has a surfaceinclined at an angle of not less than 2 degrees in the direction [011]or [0-1-1] from the plane (100) and can therefore achieve a highreflection efficiency of the multi-layer reflecting film disposedopposite to the GaAs substrate side, which reflecting film can have atthe same time a saved number of layers since the reflecting film ofAl_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1) can be easily formed with a mirrorsurface.

1. A semiconductor light emitting element, comprising: a substrate; alight emitting layer; a resonator comprising first and second reflectingfilms disposed on opposite sides of the light emitting layer, whereinthe first reflecting film comprises Al_(x)Ga_(1-x)As (0≦x≦1) and thesecond reflecting film comprises Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1);a contact layer formed on the side of the light emitting layer oppositethe side on which the substrate is provided; an insulating layer formedon the contact layer and provided with an opening therein which exposesa portion of the contact layer; and a patterned electrode formed on theinsulating layer and the exposed portion of the contact layer, whereinthe first reflecting film is disposed on the same side of the lightemitting layer as the substrate.
 2. A semiconductor light emittingelement as defined in claim 1, wherein the light emitting layercomprises one or more films of Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1). 3.A semiconductor light emitting element as defined in claim 1, whereinthe substrate comprises a GaAs substrate having a surface inclined atabout 2 degrees in the direction [011] or [0-1-1] from the plane (100).4. A semiconductor light emitting element as defined in claim 1, whereinthe resonator has a resonant wavelength of 650 nm.
 5. A semiconductorlight emitting element as defined in claim 1, wherein the length of theresonator is 1.5 times the resonant wavelength of the resonator.
 6. Asemiconductor light emitting element as defined in claim 1, wherein theopening in the insulating layer is circular.
 7. A semiconductor lightemitting element as defined in claim 1, further comprising: first andsecond cladding layers respectively formed on opposite sides of thelight emitting layer.
 8. A semiconductor light emitting element asdefined in claim 1, further comprising: a buffer layer formed betweenthe substrate and the first reflecting film.
 9. A semiconductor lightemitting element as defined in claim 1, wherein the first and secondreflecting layer each comprises a distributed Bragg reflector.
 10. Asemiconductor light emitting element as defined in claim 1, incorporatedin an optical communication network.
 11. A semiconductor light emittingelement, comprising: a substrate; a light emitting layer; a resonatorcomprising first and second reflecting films disposed on opposite sidesof the light emitting layer, wherein the first reflecting film comprisesAl_(x)Ga_(1-x)As (0≦x≦1) and the second reflecting film comprisesAl_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1); an n-type layer formed on theside of the light emitting layer opposite the side on which thesubstrate is provided and having an opening formed therein; a currentdiffusion layer formed on the n-type layer; and an electrode formed onthe current diffusion layer, wherein the first reflecting film isdisposed on the same side of the light emitting layer as the substrate.12. A semiconductor light emitting element as defined in claim 11,wherein the light emitting layer comprises one or more films ofAl_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).
 13. A semiconductor lightemitting element as defined in claim 11, wherein the substrate comprisesa GaAs substrate having a surface inclined at about 15 degrees in thedirection [011] or [0-1-1] from the plane (100).
 14. A semiconductorlight emitting element as defined in claim 11, wherein the resonator hasa resonant wavelength of 650 nm.
 15. A semiconductor light emittingelement as defined in claim 11, wherein the length of the resonator is1.5 times the resonant wavelength of the resonator.
 16. A semiconductorlight emitting element as defined in claim 11, further comprising: firstand second cladding layers respectively formed on opposite sides of thelight emitting layer.
 17. A semiconductor light emitting element asdefined in claim 11, further comprising: a buffer layer formed betweenthe substrate and the first reflecting film.
 18. A semiconductor lightemitting element as defined in claim 11, wherein the first and secondreflecting layer each comprises a distributed Bragg reflector.
 19. Asemiconductor light emitting element as defined in claim 11,incorporated in an optical communication network.
 20. A semiconductorlight emitting element, comprising: a substrate; a light emitting layer;a resonator comprising first and second reflecting films disposed onopposite sides of the light emitting layer, wherein the first reflectingfilm comprises Al_(x)Ga_(1-x)As (0≦x≦1) and the second reflecting filmcomprises Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1); a contact layer formedon the side of the light emitting layer opposite the side on which thesubstrate is provided; an insulating layer formed on the contact layerand provided with an opening therein which exposes a portion of thecontact layer; and an ITO film formed on the insulating layer and theexposed portion of the contact layer, wherein the first reflecting filmis disposed on the same side of the light emitting layer as thesubstrate.
 21. A semiconductor light emitting element as defined inclaim 20, wherein the light emitting layer comprises one or more filmsof Al_(y)Ga_(z)In_(1-y-z)P (0≦y≦1,0≦z≦1).
 22. A semiconductor lightemitting element as defined in claim 20, wherein the substrate comprisesa GaAs substrate having a surface inclined at about 15 degrees in thedirection [011] from the plane (100).
 23. A semiconductor light emittingelement as defined in claim 20, wherein the resonator has a resonantwavelength of 650 nm.
 24. A semiconductor light emitting element asdefined in claim 20, further comprising: first and second claddinglayers respectively formed on opposite sides of the light emittinglayer.
 25. A semiconductor light emitting element as defined in claim20, further comprising: a buffer layer formed between the substrate andthe first reflecting film.
 26. A semiconductor light emitting element asdefined in claim 20, wherein the first and second reflecting layer eachcomprises a distributed Bragg reflector.
 27. A semiconductor lightemitting element as defined in claim 20, incorporated in an opticalcommunication network.